1. Field of the Invention
This invention relates generally to the application of pressure relief valves to packaging for products such as coffee, and an improved apparatus and method for the application of such pressure relief valves.
2. Background Art
Pressure relief valves, such as the PLITEK PLI-VALV PV-28 pressure relief valves, are applied to packaging for products, such as coffee. These valves, which may be plastic or foil, are self-adhering, thin, low profile designs supplied on a non-tearing polyester liner. The valves have an adhesive on the back side which adheres them to the liner, until the valves are removed immediately prior to the application to the packaging, and then provides for affixing the valves to the packaging. An example of the technical properties of such valves is an opening pressure differential to pressure of 0.1375 psig (9.5 milibars) and valve closure occurs after pressure drops to 0.0375 psig (2.6 milibars). The valves vent unwanted gases and seal out atmospheric gases from rigid or flexible packaging. One advantage of such valves is that they allow coffee to be packed immediately after roasting and grinding to preserve freshness. Elimination of the holding required to allow products such as coffee to degas saves time and money, while ensuring that customers receive the highest quality coffee.
Such pressure relief valves are usually applied during the packaging process, more particularly, after the containers are formed and are being filled with the product. The packaging process may permit intermittent application of the valves, or may require that the valves be applied in a continuous operation. A system for the application of the valves generally includes a base unit, a set of guide rollers, electronic and pneumatic components, a valve oiling unit, and a valve applicator unit. The base unit provides for advancing and indexing a liner strip carrying the pressure relief valves. Conveniently, the base unit may comprise an unwinder, a rewinder (for the empty liner after the valves have been applied to the packaging), electrical components, pneumatic components, control components, and a drive motor. Guide rollers are used to orient the running direction of the liner (generally vertical or horizontal), as needed to accommodate the packaging equipment in conjunction with which the pressure relief valve applying system is being used. Electronic equipment may include sensors and stepper motors, and the pneumatic components generally include a vacuum generator, regulators and filters for feeding the vacuum and pneumatic systems, as well as valves for operating pneumatic cylinders. An oil applicator, generally positioned proximate but prior to the valve applicator unit, provides oil to activate the pressure relief valve before it is applied to the packaging. The valve applicator unit conveniently comprises a punch, piercing needle, or some other device to make an opening in the packaging, a peeler bar assisting in the removal of the pressure relief valve from the liner, and a valve applicator head for attaching the pressure relief valve to the packaging in operating register with the opening made by the punch, needle or other device. An example of such a prior art device is the ACCRAPLY Model 230 PRV Pressure Relief Valve Applicator.
A problem encountered in the prior art application of pressure relief valves to packaging, due in part to the many variables and tolerances in the processes of forming and filling the packaging, is the misalignment of the pressure relief valve with the opening with which the valve needs to be in operating register. Accordingly, there remains a need for a system with a pressure relief valve applicator for packaging in which the accuracy of the placement of the valve over, and in operating register with, the opening in the packaging is improved with respect to prior art devices.